1. Field of the Invention
This invention relates to novel salt compounds containing onium cations and non-nucleophilic complex metallate anions and more particularly, it relates to anions with at least partially fluorinated ligands coordinated to the metal. It also relates to the use of the compounds as novel initiators for the cationic polymerization of various monomers.
2. Background of the Art
Iodonium, oxonium, sulfonium, sulfoxonium, and various other onium salts are well known in the art, particularly as initiators of cationic and free radical polymerization. The effectiveness of these onium salts as initiators in cationic polymerizations, and particularly in achieving high molecular weight polymers, is known to be greatly influenced by the nucleophilic nature of the anion employed in the salt. Generally, non-nucleophilic anions function much better than their nucleophilic counterparts. This is because strong nucleophilic anions have a much greater tendency to terminate the polymer chain than do non-nucleophilic anions.
Examples of nucleophilic anions which are recognized as being detrimental counterions include fluoride, chloride, bromide, iodide, bisulfide, cyanide, bicarbonate, carbonate, nitrate, hydroxide, carboxylates, sulfonates, and trifluoromethanesulfonate (also referred to commonly as "triflate").
Examples of non-nucleophilic anions include hexafluorophosphate (1-), hexafluoroarsenate (1-), tetrafluoroborate (1-), hexafluoroantimonate (1-), tetraphenylborate (1-), and perchlorate. The use of such non-nucleophilic ions as counterions for nucleophilic sensitive cations is known, e.g., triethyloxonium tetrafluoroborate is a known stable complex. (see Meerwein, H. Org. Syn. 1966, 113, 120).
Triflate species, when paired with various materials, have been used as counterions. For example, the trifluoromethanesulfonate substituted tin centered anion is known as a counterion in organometallic complexes involving the +4 oxidation state of tin (see Mallela, et al., Can. J. Chem. 1987, 65, 2640). By further way of example, tetrakis(trifluoromethanesulfonato)iodate (1-) anion has been prepared as salts with alkali metals (see Dalziel, J. R.; Aubke, F., Inorg. Chem. 1973, 12, 2707) and tetrakis(trifluoromethanesulfonato)boric acid is known in the art for use in Friedel-Crafts alkylations (see Miethchen, R. et al., Chem. 1986, 26, 168).
U.S. Pat. No. 4,721,559 discloses the use of boron, aluminum, and gallium perfluoroalkane sulfonates as Friedel-Crafts catalysts.
U.S. Pat. No. 4,547,474 discloses the use of C.sub.10 to C.sub.18 perfluorinated alkanesulfonic acid based superacidic catalysts in various hydrocarbon conversion processes.
U.S. Pat. No. 4,472,268 discloses a process for upgrading natural gasoline by treatment with a liquid ternary catalyst system comprising trifluoromethanesulfonic acid and hydrogen fluoride in conjunction with a Lewis Acid catalyst of the formula MX.sub.n where M is selected from Groups IIIA, IVB, or V elements of the Periodic Table, X is halogen, and n is a number varying from 3 to 6.